Few things have become ruder than speech in recent years. People ignore each other and insult each other in equal measure. If society is truly to become polite again, people need to relearn how to have a civil conversation with other people. This requires people to actually respond to each other. When someone greets you, say “hello.” If they ask you a question, answer it.
Other basic speech manners include the little things that parents everywhere try to drum into children’s heads. Say “please” and “thank you” to people. When you are speaking to a stranger, introduce yourself and offer a polite handshake. If you are speaking with a coworker and your friend joins the conversation, introduce them to each other.
Perhaps the biggest thing that needs to change in modern speech is public swearing. It seems that it is impossible to walk through a shopping center without encountering at least one person who speaks almost entirely in expletives. As a general rule, if your grandmother would not approve of you saying it at the dinner table, do not say it in public.